Fix it manually – Disable the BROADCAST flag

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Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

Look at each number that is listed under the NetworkCards node in order to find the network adapter GUID. On the right side, the Description item lists the network adapter and the ServiceName item lists the corresponding GUID. Remember this GUID.

In this registry path, click the <Network Adapter GUID> subkey that corresponds to the network adapter that is connected to the network.NoteNetwork Adapter GUID is a placeholder for the network adapter GUID in this article. To find the corresponding GUID, refer to step 2 and step 3.

On the Edit menu, point to New, and then click DWORD (32-bit) Value.

In the New Value #1 box, type DhcpConnEnableBcastFlagToggle, and then press ENTER.

Right-click DhcpConnEnableBcastFlagToggle, and then click Modify.

In the Value data box, type 1, and then click OK.

Close Registry Editor.

When you set this registry key to 1, Windows Vista first tries to obtain an IP address by using the BROADCAST flag in DHCP Discover packets. If that fails, Windows Vista tries to obtain an IP address without using the BROADCAST flag in DHCP Discover packets.

By default, the BROADCAST flag in DHCP discovery packets is enabled in Windows Vista (DhcpConnEnableBcastFlagToggle = 1). Therefore, Windows Vista gets an IP address by using the BROADCAST flag in DHCP discovery packets. If a router or DHCP server can’t process the DHCP discovery packets, Windows Vista will fail to get an IP address. The fix disables the BROADCAST flag by setting DhcpConnEnableBcastFlagToggle to 0.

By default, this problem does not exist in Windows XP Service Pack 2, Windows XP Service Pack 3 or Windows 7 because the BROADCAST flag is disabled (DhcpConnEnableBcastFlagToggle = 0).

If you know the router or the non-Microsoft DHCP server does not support the DHCP BROADCAST flag, you can configure the following values for the following registry entry instead of using the DhcpConnEnableBcastFlagToggle registry key.

A value of 0 disables the registry entry. You can use this value to prevent Windows Vista from using the DHCP BROADCAST flag. After you configure the registry entry, Windows Vista never uses the DHCP BROADCAST flag.

This issue does not occur in Windows 7. By default, DhcpConnEnableBcastFlagToggle is set to 1.